Down syndrome is one of the leading causes of mental retardation and birth defects, found in one in every 660 pregnancies.
In the new screening test, a sample of the mother's blood is analyzed for the level of a protein and hormone, and an ultrasound or sonogram picture is analyzed for the thickness of skin on the back of the baby's neck. Results are available within five days.
The new test had an 87 percent detection rate, the current standard screening, a blood test performed in the second trimester of pregnancy, has an 81 percent detection rate.
So far, 1,600 physicians and sonographers nationwide are trained to conduct the new test.
The study included more than 38,000 pregnant women at 15 U.S. research centers and is published in Thursday's issue of the New England Journal of Medicine.
